This invention relates to a process for preparing certain catalytically active metal complexes. More particularly, this invention relates to such a process involving electrochemical means for conversion of a complex to an active catalytic form useful for polymerizing olefins, diolefins and/or acetylenically unsaturated monomers.
In U.S. Pat Nos. 5,064,802 and 5,132,380, cationic Group 4 metal catalysts having unique activity as addition polymerization catalysts are disclosed and claimed. In U.S. Pat No. 5,189,192, a process for single step metal center oxidation and cation complex formation of such metal complexes is-disclosed. In pending U.S. application U.S. Ser. No. 547,718, filed Jul. 3, 1990, there is disclosed a molecular oxidative activation procedure for preparing the same or similar complexes. For the disclosures contained therein the preceding pending application and issued patents are hereby incorporated by reference in their entireties.
In the above oxidation processes, a chemical oxidizing agent is employed to convert the initial metal complex to the active catalytic species. Such chemical oxidizing agents result in the generation of byproducts that may be environmentally unacceptable and are desirably removed from the resulting catalyst product. Such removal step complicates the preparation method.
In Inorg. Chem., 31, 5345-5346 (1992), the one-electron electrochemical oxidation of biscyclopentadienyltitanium dichloride in acetonitrile solvent using tetrabutylammonium tetrafluoroborate supporting electrolyte is disclosed. The tetrafluoroborate counter ion is a coordinating ligand and the acetonitrile solvent is both reactive and coordinating under the conditions of the electrolysis. Accordingly, the resulting cationic product, biscyclopentadienyltitanium chloro acetonitrile tetrafluoroborate (Cp.sub.2 TiCl(CH.sub.3 CN)+BF.sub.4-) is not catalytically active for addition polymerizations.
The present invention lies in the discovery of a novel electrochemical technique for preparing certain catalytically active Group 4 metal complexes. By electrochemical activation, an improved and greatly simplified method of catalyst preparation is provided. Moreover, the present process does not result in formation of byproducts from chemical oxidants that contaminate the desired catalyst. Further, due to the absence of coordinating or reactive species in the reaction, a highly active addition polymerization catalyst is produced. Finally, since the electrolysis may be monitored to achieve precise conversion of only the desired materials, no excess oxidant is left in the resulting product. Thus, a highly efficient method for preparing the desired metal complexes is provided.